Metallic copper or silver sintering

sintering line

Metallic sintering with copper or silver pastes has proven to be a highly reliable alternative to soldering. Especially the pressure-assisted sintering process delivers superior results in regards to cycle times, application temperature and lifetime, compared to soft soldering. However, in order to achieve a reliable connection, a pressure-force of 10 to 30 MPa is required. Moreover, a precise temperature control and clean surfaces are mandatory for a high-quality sinter joint.

We offer advanced silver and copper sintering training opportunities with a holistic view on the sintering line, as well as workshops dealing with and boundary conditions, such as material quality.

Possible training and project contents:

  • Suitable-for-production product design for sintering processes
  • Development of temperature and pressure profiles
  • Typical faults during drying, printing and sintering
  • Temperature and pressure measurement techniques, as well as sources of errors
  • Influence of previous processes on sintering
  • Material quality, tools and system checks with rapid testing functions
  • Identification of save process windows
  • Transfer of laboratory processes to mass production
  • Introduction of inline measurements and statistical process controls
seminars for data science

History of silver sintering (low temperature joining technology LTJT)

Originally published by Schwarzbauer in 1989, in recent years metallic silver sintering has proven to be a much more reliable alternative to soft soldering in power electronics. In addition to numerous dissertations, several industrial companies have also dealt with the subject and are currently working on transferring the process to series production.

Sintering is generally a process technology to produce materials with a certain density from metallic or ceramic powders by means of thermal energy. The driving force of sintering is that a powder passes from a high-energy to a lower-energy state. This is done by minimizing the surface energy of the particles through the sintering process. This process is accelerated by pressure and temperature.

Metallic silver sintering is solid phase sintering. Here, particles are present in paste form together with encapsulating and dispersing agents as well as organic binders. The paste is applied to the substrate by stencil or screen printing or by dispensing and then dried. The chip is sintered to the substrate by the silver particles in one to two minutes at a pressure of up to 50 MPa and temperatures of 200 °C to 300 °C.

Since the sintering reaction takes place at a temperature significantly below the melting temperature, the process is also known as low-temperature joining technology (LTJT). In most cases, LTJT requires a precious metal surface of the joining partners, whereby sintering pastes for copper surfaces are currently under development. The LTJT shows an order of magnitude better temperature and power cycling capability. The reason for this is the electrical and thermal conductivity, which is four times higher, as well as the five times higher yield strength and the 15% lower thermal expansion of pure silver compared to SAC solders. At 962 °C, the melting point of silver is significantly higher than that of soft solder alloys. This makes the material ideal for high temperature applications.

Articles about copper and silver sintering:

Do you have further questions regarding metallic sintering? Do not hesitate to contact us!